1. Field of the Invention
This invention relates to methods of encoding data such as found in motion picture video and audio.
2. Description of Related Art
The desire to distribute and display motion pictures in digital form, such as by means of a computer system, has led to the development of the MPEG ("Motion Pictures Experts Group") standards for motion picture video data. The MPEG standards prescribe a set of variable-length structures for encoding motion picture video and audio data, which may be read by and interpreted by a digital processor so as to display motion pictures. The MPEG standards have the advantage of providing substantial data compression of motion picture video data. However, the MPEG standards do not provide a convenient and effective method for encoding motion picture video and audio data so that such data cannot easily be copied by unauthorized persons.
Known methods of encoding data so that unauthorized persons cannot copy that data generally involve manipulating the data by a transformation, so that a password or key is required to perform a necessary inverse transformation, so as to obtain the original data. While these methods achieve security of the data, they are generally subject to certain drawbacks. (1) Errors in data distribution, or in data storage, may render the transformed data useless, because the inverse transformation is unable to recover the original data. (2) The transformation may be ill-suited to data structures which have variable length. In the case of the MPEG standards, the large amount of data involved may transform these drawbacks into serious engineering issues. First, the large amount of data greatly increases the likelihood that there will be at least some errors in distribution or in data storage. Second, the MPEG standards provide for data fields which are highly interdependent.
Accordingly, it is an object of the invention to provide methods of encoding data in variable-length data structures, such as those found in motion picture data, in which the encoded data may be difficult for unauthorized persons to copy, but in which the encoded data is easily decoded and displayed in a real-time video and audio display, and in which the encoded data is less subject to errors in data distribution or data storage.